In a sine-wave driving mode (180-degree conduction mode) known as a driving mode for a synchronous motor such as a three-phase DC brushless motor, a rotor position is detected without a sensor in order to appropriately carry out a conduction to a stator coil without a sensor.
Patent Literature 1 discloses a rotor position detection method in which a first phase difference between a motor current and an actual rotational position is found and a second phase difference between a motor current and a virtual rotational position is found; and a phase error between the actual rotational position and the virtual rotational position is estimated on the basis of the difference between the first phase difference and the second phase difference; and a voltage frequency is corrected so that the phase error reaches zero.
Patent Literature 2 discloses a rotor position detection method in which a rotational angular velocity, a d-axis current, and a γ-axis current of a synchronous motor are found; and an estimated rotation angle is fond on the assumption that an angular deviation between an actual rotation angle of a rotor and a rotation angle estimated based on a rotation model is proportional to a current deviation between the d-axis current and the γ-axis current.
The rotor position detection methods disclosed in Patent Literatures 1 and 2 basically detect a desired rotor position by correcting a virtual rotor position under predetermined conditions. Therefore, the rotor position detection accuracy varies depending on the correction accuracy. Further, the rotor position detection methods require repeating a process of finding the virtual rotor position and then correcting the rotor position at high speeds. Therefore, a high performance data processing apparatus corresponding to a high processing load is needed.